1. Field of the Invention
The present invention relates to a device and method for the inspection of the condition of a sample. In particular, the present invention relates to a device and method utilizing a simple arrangement of a stationary radiation source for directing polychromatic radiation such that the radiation is incident on the sample in parallel or diverging rays, and a position-sensitive, energy-sensitive detector for measuring components of the reflected radiation to efficiently and effectively inspect the sample.
2. Description of the Related Art
A method of this kind and corresponding devices are known, for example, from DE 41 37 673 A1 which discloses a reflectometer whereby radiation that is bundled on and reflected from a point of a sample to be inspected is measured simultaneously in different zones a position-sensitive detector; information concerning the density, roughness and thickness of a surface layer of the sample can then be derived therefrom. Therein, the angle of incidence of the radiation is chosen so as to be fixed, that is, near the critical angle for total reflection. In comparison with known goniometers, the device offers the advantage that the angle of incidence of the radiation source need not be varied during the measurement and that hence the position of the detector need not be adapted either. It is a drawback of such a reflectometer, however, that each time only a very small, almost punctiform area of the sample can be inspected. In order to derive information concerning a larger area of the sample, therefore, it is necessary to perform a time-consuming plurality of measurements. The focusing of the radiation, moreover, imposes the risk of modification or damaging of the surface of the sample.
Therefore, the invention thus has for its object to modify a device of the kind set forth above and a corresponding method such that a larger area of the sample can be inspected within a short period of time
This object is achieved in accordance with the invention by means of a device and a method having a stationary radiation source for directing polychromatic radiation such that the radiation is incident on the sample in parallel or diverging rays, and a position-sensitive, energy-sensitive detector for measuring components of the reflected radiation.
Because the radiation source is constructed and oriented in such a manner that the radiation is incident on the sample in parallel or diverging rays, a larger area of the sample can be irradiated at the same time; the rays are reflected from said larger area and reach different zones of the detector, each detector zone or each measuring cell of the detector corresponding to a given area on the surface of the sample. When the detector is constructed so as to be energy-sensitive in addition to position-sensitive, an energy-dependent spectrum can be measured in each detector zone or in each detector measuring cell, said spectrum providing information concerning the condition of the sample in the corresponding area. When the radiation source is constructed and arranged in such a manner that it irradiates an essentially linear area on the surface of the sample, for example, by way of parallel orientation of the radiation in one direction only, the reflected radiation that is incident on the detector can be simply related to the corresponding area on the surface of the sample. It is then advantageously possible to use an essentially linear detector in which the individual detector cells are arranged linearly adjacent one another and which is oriented so as to match the linearly irradiated area on the surface of the sample. The use of polychromatic radiation enables the acquisition of information concerning the thickness and surface roughness of the sample material and the thickness of, for example, a surface layer by application of Bragg equations for the examination of the interference phenomena. X-rays having the complete wavelength spectrum are preferably used for this purpose; radiation having a partly reduced spectrum, that is, wherefrom the source peaks have been filtered out, however, can also be used.
Favorable measuring results can be obtained by means of the measuring device in accordance with the invention and the method in accordance with the invention notably when the angle of incidence of the radiation on the surface of the sample is chosen so as to be close to the critical angle for total reflection. Therefore, radiation angles of incidence of between approximately 0.3xc2x0 and 1.5xc2x0 are preferably used. When diverging radiation is used, in which case the individual rays are incident on individual points on the sample surface at different angles of incidence, the radiation source should be positioned or oriented in such a manner that the angles of incidence of the individual rays on the sample lie approximately in the stated range of between 0.3 and 1.5xc2x0. The use of an at least approximately punctiform radiation source enables optimum measuring results to be obtained.
An essentially linearly irradiated area on the sample can be realized, for example, by collimating in one direction the radiation that is directed onto the sample, for example, between plates that are oriented perpendicularly to the plane of the surface of the sample, so that the line-shaped irradiation area on the surface of the sample is formed in the direction of an imaginary connecting line between the radiation source and the sample. The distance between such collimating plates preferably amounts to approximately 200 xcexcm. The radiation can then be considered to be substantially parallel between the plates while a strip of adequate width is still irradiated on the sample, thus ensuring an adequate intensity for the energy-sensitive measurement. The device in accordance with the invention offers a good and fast measurement notably when an area whose length amounts to approximately twenty times its width is simultaneously irradiated on the sample. For example, when use is made of a radiation source that has a radiation angle or maximum divergence angle of 0.02xc2x0, a strip of 40 mm length will be simultaneously irradiated by a beam that is oriented in parallel in one direction when the distance between the radiation source and the surface of the sample amounts to 100 mm.
In order to enable the undesirable effects of diffuse scattered radiation to be taken into account for the measurement, at least one further position-sensitive, energy-sensitive detector can be arranged adjacent the first detector in such a manner that this further detector is not exposed to the directly reflected radiation but only to the diffuse scattered radiation. The energy values measured by the first detector can be corrected for the scattered radiation component by subtracting therefrom the values that have been measured by said further detector. Preferably, a further detector is provided to each side of the first detector, the detectors preferably being oriented in parallel in order to ensure that the measured results can be readily evaluated. This object is also achieved in a particularly simple manner by means of a two-dimensional detector, that is, a detector having position-sensitive, energy-selective detector cells that are arranged adjacent one another in a two-dimensional array instead of in a linear one-dimensional array.